Exam 28: Sources of Magnetic Field

Double-slit interference: In a double-slit experiment, the slit separation is 2.0 mm, and two wavelengths, 750 nm and 900 nm, illuminate the slits simultaneously. A screen is placed 2.0 m from the slits. At what distance from the central maximum on the screen will a bright fringe from one pattern first coincide with a bright fringe from the other?

X-ray diffraction: Certain planes of a crystal of halite have a spacing of 0.399 nm. The crystal is irradiated by a beam of X-rays. First order constructive interference occurs when the beam makes an angle of 20° with the planes. What is the wavelength of the X-rays?